In recent years, the elements, devices, modules, apparatus, or instruments for detecting the interactive gestures, postures or 3D scanning trajectories have been increasingly developed. Particularly, an infrared (IR) structured light may be employed to achieve the above detecting function, although the wavelength of IR band may be selected to be the less appeared in our environment. The structured light is generally developed with a finite cone of specific solid angle such that the interactive actions can be well recognized within the cone. On the other hand, a planar scanning structured light is also provided for recognizing the interactive actions or the important indicating objects. The structured pattern can be generated by diffractive element for a fixed pattern or projection device such that the pattern can be changed as required. Overall, to have better brightness contrast, the light of laser is considered. For a laser light emitter, the light is generally with a divergence angle, while for many application circumstances the light has to be collimated. As a result, a collimated infrared light is necessary to be achieved in advance for realizing the function. However, since the current laser diode module with the function of generating the collimated light has bulky volume, this laser diode module cannot meet the requirements of the modern slim type mobile phone, wearable devices, and so on.
On the other hand, the current laser diode module is usually equipped with a dust-proof lens at a side of a housing thereof. In some situations, the dust-proof lens may be omitted. However, if the dust-proof lens is omitted, the optical path length or the working distance is possibly changed. The change of the optical path length or the working distance may adversely affect the operation of the laser diode module. Therefore, it is important to install a compact-size and user-friendly structured light generation device in a mobile phone so as to achieve the 3D gesture or scanning function. Meanwhile, because of the volume of device becomes small, for the optical element its corresponding effective focal length (f), back focal length (bfl), and working distance (WD) have to be small, and then the tolerance becomes critical for such a compact-size device. In other words, the device has to be able to perform well enough for a range of values of working distance (or, effective focal length, or back focal length), not just a fixed value. When the design is workable for a range of parameters, so as to that with different of optical paths.